In general, an oxygen enrichment apparatus of such type has been used in medical fields. A conventional oxygen enrichment apparatus, however, should control concentration of oxygen in high precision; therefore, cost of the oxygen enrichment apparatus is high and size thereof is large. Accordingly, the conventional oxygen enrichment apparatus cannot be used readily by common people.
There has been proposed in Japanese Patent Laid-Open No. 1998-234836 an oxygen enrichment apparatus which can be readily used by common people. The oxygen enrichment apparatus includes an oxygen enriching membrane accommodated within a main body, a pump for suctioning oxygen-enriched air through the oxygen enriching membrane, and a discharge port through which the oxygen-enriched air is supplied to a user.
However, since this oxygen enrichment apparatus is designed to have an air cleaning function as well, there still is a limit in reducing the size and the price thereof and common people can hardly afford it.
Further, the oxygen-enriched air is supplied to the user mixed with air discharged from an air cleaning unit and, therefore, the oxygen concentration of the air inhaled by the user is not so high due to dilution of the oxygen therein.
Furthermore, since the oxygen enriching membrane is likely to transmit moisture in the air together with the oxygen, it frequently happens that moisture in the oxygen-enriched air is condensed and the condensed water is discharged with the oxygen-enriched air, thereby discomforting the user. In case zeolite is employed instead of the oxygen enriching membrane, maintenance thereof becomes troublesome.